1. Field of the Invention
This invention relates to an ink jet recording apparatus of the continuous jet type, and more particularly to adjustment of an ink jet jetting axis (nozzle axis) of a continuous jet type ink jet recording apparatus.
2. Description of the Prior Art
Various ink jet recording apparatus of the continuous jet type are conventionally known and practically used. An exemplary one of such conventional continuous jet type ink jet recording apparatus is shown in FIG. 9. Referring to FIG. 9, the continuous jet type ink jet recording apparatus shown includes an ink bottle 91 in which ink is accommodated, an ink pump 92 for applying a pressure to ink from the ink bottle 91 and sending out the thus pressurized ink, an ink tube 93 for supplying ink from the ink pump 92 therethrough, a nozzle 94 having a circular orifice of a very small diameter, an ink electrode 95 for holding the potential of ink in the nozzle 94 at a ground level, an oscillating element 96 in the form of a piezoelectric oscillating element mounted on the nozzle 94, an oscillating element driving oscillator 97 for applying an exciting signal to the oscillating element 96, a controlling electrode 98 having a circular opening or a slit-like opening coaxial with the nozzle 94 for receiving a controlling signal to control charging of a jet of ink, a grounding electrode 99 disposed in front of the controlling electrode 98 and grounded itself, a knife edge 100 mounted on the grounding electrode 99, a deflecting high voltage dc power source (hereinafter referred to as deflecting power source) 101, and a deflecting electrode 102 connected to the deflecting power source 101 for cooperating with the grounding electrode 99 to produce therebetween an intense electric field perpendicular to an ink jet flying axis to deflect a charged ink drop to the grounding electrode 99 side. The thus deflected charged ink drop is flown to a record medium 104 wrapped around a rotary drum 103.
In such conventional continuous jet type ink jet recording apparatus, ink pressurized by the ink pump 92 is introduced by way of the ink tube 93 into the nozzle 94, at which a jet of the ink is formed from the orifice. The ink jet is disintegrated into a train of ink drops with a spontaneous disintegrating frequency which depends upon a diameter and a flow rate of the ink jet and physical properties of the ink. In this instance, if the exciting frequency of the oscillating element 96 mounted on the nozzle 94 is set to a value at or around the spontaneous disintegrating frequency, then disintegration will be synchronized with excitation of the oscillating element 96, and consequently, ink drops of a very uniform size are produced with the exciting frequency.
If such uniform ink drop train is binary charge modulated in accordance with a controlling signal (recording pulses) having a phase synchronized with the exciting signal, then a charged ink drop will be deflected toward the grounding electrode 99 side by an action of the deflecting electric field produced by the deflecting electrode 102 and then cut by the knife edge 100, but an uncharged ink drop advances straightforwardly above the knife edge 100 to record a dot on the record medium 104 wrapped around the rotary drum 103. Accordingly, if the controlling signal is made correspond to a printing signal or an image signal, then a character or an image is recorded in a binary fashion on the record medium 104.
In order to control on-off of recording correctly and stably with a controlling signal or voltage supplied to the controlling electrode 98, it is necessary to provide a sufficient amount of deflection to an ink jet and to set the positional relationship between a jetting axis of the ink jet (nozzle axis) and the knife edge 100 to an optimum one.
The amount of deflection of an ink jet is designed, with a conventional continuous jet type ink jet recording apparatus which has been put into practical use, such that an ink jet is charge modulated with 40 to 150 volts and the amount of deflection above the knife edge 100 ranges from 0.1 to 0.4 mm.
In order to allow adjustment of the ink jet jetting axis (nozzle axis), a conventional continuous jet type ink jet recording apparatus which has been put into practical use has such a structure, for example, as shown in FIG. 10 wherein the nozzle 94 is normally urged by a compression Spring 112 upwardly in FIG. 10 to contact with an adjusting screw 113 so that it can be independently adjusted around a fulcrum 111 with respect to the knife edge 100 by means of the adjusting screw 113. Thus, the ink jet jetting axis (nozzle axis) is adjusted manually and mechanically.
The amount of deflection of an ink jet increases in proportion to a controlling voltage applied to the controlling electrode 98. Accordingly, the position of the ink jet jetting axis (nozzle axis) is optimum when an end of the knife edge 100 coincides with a medium point between ink jet flying axes that the ink jet presents when the controlling voltage is on and off. However, it is almost impossible to adjust, in a real machine, the ink jet jetting axis (nozzle axis) by observation of an ink jet flying axis by means of a microscope.
Actually, therefore, the continuous jet type ink jet recording apparatus is rendered operative to perform test printing while the adjusting screw 113 is operated manually to adjust the position of the nozzle 94.
Also an ink jet recording apparatus of the continuous jet type has been proposed and is disclosed, for example, in Japanese Patent Laid-Open Application No. 2-1322 wherein the amount of substantial deflection of an ink jet by a deflecting electric field when relative positions of such ink jet and a gutter member (which corresponds to or is equivalent to a knife edge) are to be set and adjusted is reduced (for example, to one half) from that when normal recording is performed. With such continuous jet type ink jet recording apparatus, a determination of whether or not an ink drop collides with the gutter member can be made readily by connecting a charge amount detector to the gutter member and monitoring an output of the charge amount detector.
With the conventional continuous jet type ink jet recording apparatus described first hereinabove, since actually it is rendered operative to perform test printing and the adjusting screw 113 is manually operated, during such test printing, to adjust the position of the ink jet jetting axis (nozzle axis), there is a problem that such adjustment is qualitative and identification of such medium point between ink jet flying axes as mentioned hereinabove is impossible. In particular, since an instant at which an ink jet collides with the knife edge 100 can be identified in the process of adjustment, it will be a limit in reduction to practice to presume a position of the nozzle 94 from a rotational angle of the adjusting screw 113 with reference to the position of the knife edge 100 then. If the adjusting screw 113 has some backlash, then identification of the medium point will be further inaccurate.
Further, since actually the adjusting screw 113 is manually operated to adjust the position of the nozzle 94 while the continuous jet type ink jet recording apparatus is operating, there is another problem that mechanical and electrical risks are involved.
Furthermore, since a record medium is consumed for adjustment of the position of the nozzle 94, there is a further problem that it is uneconomical.
In addition, it is also disadvantageous that, if an ink jet collides with an end of the knife edge 100 in a record area, then the rotary drum 103 or the like will become soiled.
On the other hand, with the second conventional continuous jet type ink jet recording apparatus wherein the amount of substantial deflection of an ink jet by a deflecting electric field when relative positions of an ink jet and a gutter member are to be set and adjusted is reduced from that when normal recording is performed, since the number of parameters of deflection upon adjustment is only one, there are drawbacks that it cannot be confirmed by what degree of accuracy the amount of deflection is adjusted, that precise adjustment is impossible if the mechanical accuracy is not high, that, if the mechanical accuracy is made high, then the continuous jet type ink jet recording apparatus will be high in production cost, and so forth. Especially, while the gutter member must have an insulating structure when a charge amount detector is connected to the gutter member, since the gutter member is always exposed to ink, there is a problem that much difficulty and complication in structure are involved in such insulating structure.